text:
Why wasn't Solar Impulse 2 cleared for takeoff?
I've recently been watching videos of the Solar Impulse 2 (HB-SIB) flights, and I noticed that on several occasions, instead of giving clearance for takeoff, the tower told the pilot that "departure is at your own risk".
In particular, this happened at Kalaeloa (PHJR) in Hawaii, at Dayton (KDAY) and at Lehigh Valley (KABE).
But, at Moffett Field (KNUQ), Tulsa (KTUL), and out of KJFK, the flight was "cleared for takeoff".
I couldn't spot anything obvious in the tower conversations to suggest why departure was at the pilot's own risk. Out of KDAY, the tower said that the runway the plane was using was closed (of course it's closed, there's an experimental solar airplane and ground crew on it), and at KABE the tower mentioned a jet that landed on the other runway a few minutes prior.
What happened here? Why was departure at the pilot's own risk?

Perhaps the presence of a ground crew caused the runway to revert to something other than a "legal" runway. Maybe the controllers, unwilling to fromally clear a plane for takeoff from something other that a legal runway, opted instead to tell the pilot to "go on and give it a whirl if you think it's safe." I wish I knew the answer...good question.

@acpilot Maybe. But the crew was present at all of these departures. At JFK (and several others) you can clearly see bicycles on the runway as he gets clearance for takeoff!

Could be as simple as a controller succumbing to force of habit. Plane on runway usually equals "cleared for takeoff." Being caught up in the moment and dealing with a goofy situation could trip people up.  I'm looking forward to learning the right answer!

"Roger tower -- I'm going to cross the ocean in this thing. I think that is risky."

Holy f… that thing is slow! And how short was that takeoff roll? Why do they even close a runway for that thing, you could get it airborne by just sneezing at it!

@JörgWMittag Pretty close. It takes off at 20 knots whether you rotate or not. But it also climbs rather slowly.

Interesting question. The ATC orders mention only two reasons that controllers have to say "at your own risk":

The pilot "insists" on using a closed or unsafe runway (3-3-2)
A helicopter takeoff or landing uses a non-movement area (3-11-2, 3-11-6)

Obviously Solar Impulse 2 isn't a helicopter, so that leaves the closed or unsafe runway reason. I don't know for sure why the tower used the "own risk" phraseology - it would be great to hear from an actual controller - but some possibilities are:

The runway was marked as closed (for Solar Impulse 2) on the tower controller's displays, and he said "at own risk" more or less out of habit
There were vehicles on the runway, therefore it was "unsafe"
Solar Impulse 2 is such an unusual aircraft that the controller felt he couldn't contribute anything to the safety of the takeoff, so he was simply saying "go for it, I can't do much to help you"

Of course, the problem with all those suggestions is that they should apply at all the airports, not just half of them. But I did find this quote from a controller on the AOPA forums (members only):

Although it's normal for helicopters, I issued this "departure will be
  at your own risk" to an aircraft once. The runway was open, he wasn't
  departing from a taxiway or anything like that. The problem was fog,
  where I couldn't see the runway from the tower, and therefore I
  couldn't determine whether the runway was actually "clear" for his
  takeoff.
I don't know if this is the right response in this situation or not,
  but I was a pretty new controller at the time, hadn't faced this
  situation before, and figured the "at your own risk" was appropriate.

That could have applied to the Solar Impulse situation: with other vehicles and personnel on the runway, the controller can't say it's "clear". And just like the controller on the forum, perhaps some of the controllers handling Solar Impulse 2 felt that the non-standard wording was appropriate for a very unusual situation. The other controllers who did issue a takeoff clearance presumably felt differently.

authors: Μπάμπης Παπασπύρος

authors: Михаил Ушкалов


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What benefit does a group get from being an FAA recognized flying club?
FAA defines a flying club in 5190.6b.ch10.6 and ends by saying:

A flying club that violates the requirements for a flying club – or that permits
  one or more members to do so – may be required to terminate all operations as a flying club at all airports controlled by the airport sponsor.

So hypothetically if this were to occur, then you'd have an LLC that owns a plane that is not a flying club. Does this mean that they wouldn't be able to fly their plane or carry on like normal? Aside from being able to label themselves as a "Flying Club", what impact would this have?

they would be able to advertise a vested interest in keeping the FAA "seal of approval"

If the airport you're based at has federal grant obligations (basically if they've taken money from the Airport Improvement Program) then being a "flying club" by the FAA's definition entitles you (as a group) to the same rights as any other operator at the field (like the right to fuel your aircraft with fuel you buy yourself & have trucked in, or the right to do maintenance on the aircraft), subject to the same rules and regulations the airport lays down for all operators.
The biggest material difference is that "flying clubs" aren't considered to be "commercial" ventures by the FAA (and by extension grant-obligted airports).
As an example, let's say you have a flying club & you "charge" $50/hr for the use of one of the planes, and your airport management decides that since you're charging money for the use of the planes you're a commercial venture, and need to have commercial insurance and the like.
If you meet the FAA definition of a "Flying Club" and the airport has federal grant obligations you can ask your local FSDO to step in and effectively tell the airport management to get stuffed - as a flying club you're treated more like an individual than a commercial business, and the airport is not allowed to impose those commercial requirements on you.
If you don't meet that definition the FAA won't intervene on your behalf (as far as they're concerned you are a rental outfit / commercial FBO at that point and the airport is correct in treating you as one).

Note that you can still call yourself a "flying club" even if you don't meet the FAA's definition -- I belong to a flying club that has no aircraft (we're just a bunch of folks who like to talk about flying and organize the occasional fly-out event or safety seminar - some of us own planes, and some rent from local FBOs), and it doesn't really matter to us that we don't meet the FAA definition of a flying club because we don't have any interaction with the airport where that designation would benefit us.
If you're the kind of organization that has aircraft available for the use of your members however it probably makes sense to ensure that you're organized & run in such a way as to meet the FAA definition of a flying club.

source: Stack Exchange

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sort: votes


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What is a fuel tank float valve and how does it work?
This report on dodbuzz mentions a 'fuel tank float valve'. Neither google nor StackExchange seem to know what it is. What is it, why is it necessary?

I don't know about the fuel float valve of the F35A. A float valve is basically the principle used in toilet flush: A device that:

senses liquid level in a tank, and
open/close a valve according to this level.

The device may rely on a float acting on a horizontal lever, or it may be a float sliding vertically along a rod.
There are several float valves on this schematics of the Boeing 737 fuel system:

Source
If this doesn't work, the tank may be reported as always full, as for the F35A of your report.

Thanks for your answer, I'll wait a little longer, before accepting...

While floats (though not float valves) are used in many light aircraft to sense fuel levels, most larger or turbine aircraft use capacitance level sensors with temperature compensation. Some aircraft also use floats for tank level sensing for fuel transfer purposes.

An aircraft fuel system uses float values in the fuel vent system.  This is to ensure the fuel is vented regardless of the attitude of the aircraft or the quantity of fuel on board. Especially on larger aircraft and in larger tanks, there will be multiple vent locations in the same tank.
From AMT Airframe Handbook (FAA-H-8083-31) Chapter 14 Aircraft Fuel Systems

Going to take a bit of a stab in the dark on this one...
I'm presuming the float valve mentioned is the one connected to a fuel measuring stick.
In the middle of a magnetic level indicator there is a float valve external of the stick housing which contains a magnet. The indicator rod also has a magnet at the upper end I.e. The end closest the fuel. When the rod is lowered out of the bottom of the fuel tank a magnetic coupling occurs between rod and float and the level of fuel in the tank may be read off from the calibration intervals on the rod.

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Why do civil aviation aircraft not routinely carry missile defense systems?
With all the incidents with civil aircraft and missiles, why do civil aircraft not carry flares and other defensive measures by default? If official aircraft carry them it is technically possible to fit them, isn’t it? With the possible fallout and the enormous loss of life, why do air defense systems allow the operators to target civil aircraft in the first place?

Does this answer your question? Why don't airliners carry radar jamming technology or missile counter measures?

See also https://aviation.stackexchange.com/questions/66587/why-dont-commercial-aircraft-adopt-a-slightly-more-seaplane-like-design-to-allo

"All the incidents"? I count 39 in over 80 years. Of those, 1 missed the target, so a missile defense system was not necessary, 8 were attacked with guns, 1 with artillery, so a missile defense system wouldn't have helped, 3 were attacked on the ground, 1 is only rumoured but not proven to be hit by a missile, 1 was an "unknown projectile", several were light aircraft that don't have the power and space to install missile defense systems, 2 stretch the definition of "civilian" (they were Cuban-Americans illegally violating Cuban airspace to drop anti-government propaganda leaflets).

And for why missile systems allow civil aircraft to be targeted, 1) How do you reliably tell the difference between military & civil aircraft? 2) If there WAS some reliable way - say transponder codes for a simple example - wouldn't anyone wanting to carry out a sneak attack simply masquerade as a civil aircraft? 3) There are circumstances, such as a repeat of 9/11, where you might want to shoot down civil aircraft.

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What happens to ADIRU/FAC AP etc, when Pitot probes fail?
Situation: Suppose due to a bird strike pitot 1 is blocked with debris and radome is dented causing inconsistent airspeed indication between P2 and P3 (due to unequal airflow). This happens at about FL50 before landing. Aircraft is A320 neo.
Will the ADIRU 1 be operational? Since only ADR 1 is failing due to blocked P1 and IR 1 is still functioning. Capt. lose his airspeed indication. He can switch to ADIRU 3 but inconsistency will be seen. What systems will fail due to this? How FAC respond? I think Autopilot will be out...
Help: Can anyone be explain what will happen in this scenario?

"I think Autopilot will be out", it will as airspeed is not reliable. A320 FCOM cited here: "If one ADR is faulty, or has been rejected by the ELAC, and if there is a speed or alpha disagreement between the 2 remaining ADRs, alternate law becomes active, and protections are lost." There are more details in the forum linked. See AF447 BEA report, from 1.16.3.1 Analysis of the initial sequence. See also this question

With the following assumptions:

ADR1 non operational (self-detected a failure)
ADR2 and ADR3 operational but speed discrepancy
Pilots do not turn off ADR2/ADR3

Let's analyze each system (quotes are from an A320neo FCOM).
IRs
IRs are independent systems and not affected by failures of ADRs:

Each ADIRU is divided in two parts, either of which can work separately in case of failure in the other

ADR 1 failure
The list of inoperative systems when ADR1 fails are:

ADR 1
CAT 3 DUAL
GPWS

So, ADR1 obviously, you can't use the CAT 3 autopilot landing, and GPWS is not working. There will be also several automatic "invisible" switches. For instance, primary TCAS will switch from ADR1 to ADR3.
Disagreement on the remaining ones
In this case, the remaining ADRs will still continue to provide data to the systems but:

In the case of subsequent, significant, speed discrepancy between the
two remaining ADRs, the “ADR DISAGREE” ECAM caution will trigger.

If we look at the inoperative systems when ADR DISAGREE occurs we have:

RISK OF UNDUE STALL WARN
F/CTL PROT

ALTN LAW: PROT LOST
WHEN L/G DN: DIRECT LAW

So, the flight law switches to alternate law and this will further degrate into direct law when the landing gear is down.
What happens to autopilot
The FCOM doesn't explicitly state what happens to AP, but in this incident report I found:

AP is available only if both FACs consider at least two ADRs valid.

To be considered valid they must provide a similar value. Then, no AP available in the considered scenario.

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What is area in equation of lift?Does it remain constant during flight?
I am beginner & learning aerodynamics concept. What is area in equation of lift(L) =Coffecient of lift x area x density x square of velocity/2. Does increase in angle of attack increases the area & thus increasing lift?

This area is called a reference area, and for serving as a reference it is helpful that it doesn't change. Here and here are answers which you should find helpful.

This really is two separate questions also.

The área $A$ in lift equation $L=\frac{1}{2} \rho AV^{2}C_{L}$ is a reference area, so you can choose the one you prefer, but some election can be more apropiate than others depending on what you want to compute. For example if you are going to relate lift coefficient with drag one, the reference area should be the same, in this case a good selection will be the projected area in lift direction (aka planform area). It has the drawback that it depends on angle of attack/incidence since the true area is the same but lift vector changes. Another well selected area could be the true area (aka wetted) when working with drag, specially when friction drag is dominant considering that viscous stresses are proporcional to this area.
I give you some references when this is better explained:

There are several different areas from which to choose when developing the reference area used in the drag equation. If we think of drag as being caused by friction between the air and the body, a logical choice would be the total surface area (As) of the body. If we think of drag as being a resistance to the flow, a more logical choice would be the frontal area (Af) of the body which is perpendicular to the flow direction. This is the area shown in blue on the figure. Finally, if we want to compare with the lift coefficient, we should use the same area used to derive the lift coefficient, the wing area, (Aw). Each of the various areas are proportional to the other areas, as designated by the "~" sign on the figure. Since the drag coefficient is determined experimentally, by measuring the drag and measuring the area and performing the necessary math to produce the coefficient, we are free to use any area which can be easily measured. If we choose the wing area, the computed coefficient has a different value than if we choose the cross-sectional area, but the drag is the same, and the coefficients are related by the ratio of the areas. In practice, drag coefficients are reported based on a wide variety of object areas.

Size effects on drag - NASA

A comment is in order regarding the reference area Sin Eqs. (2.3) to (2.5). This
  is nothing other than just a reference area, suitably chosen for the definition of the
  force and moment coefficients. Beginning students in aerodynamics frequently want
  to think that S should be the total wetted area of the airplane. (Wetted area is the
  actual surface area of the material making up the skin of the airplane-it is the total
  surface area that is in actual contact with, i.e., wetted by, the fluid in which the body
  is immersed.) Indeed, the wetted surface area is the surface on which the pressure
  and shear stress distributions are acting; hence it is a meaningful geometric quantity
  when one is discussing aerodynamic force. However, the wetted surface area is not
  easily calculated, especially for complex body shapes. In contrast, it is much easier
  to calculate the planform area of a wing, that is, the projected area that we see when
  we look down on the wing.

Aircraft performance and design - John D. Anderson


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Is it possible to have an angle of incidence for a vertical stabilizer?
horizontal surfaces in airplane have small angle of incidence in general, Is it possible to have an angle of incidence for a vertical stabilizer?
Please help me to find it. Thanks!!

You may be french-speaking. In English, you usually use "angle of attack" while in French you use "angle d'incidence"

NO :the angle of incidence (sometimes referred to as the mounting angle[1]) is the angle between the chord line of the wing where the wing is mounted to the fuselage, and a reference axis along the fuselage (often the direction of minimum drag, or where applicable, the longitudinal axis). The angle of incidence is fixed in the design of the aircraft, and with rare exceptions, cannot be varied in flight.

Yes, but the term "incidence" normally only applies to horizontal surfaces. With a fin it's usually called "fin offset" and is very common on single engine tractor aircraft.
The offset helps align the fin into the spiraling airstream coming off the prop so that a counteracting rudder input isn't required (or at least a smaller input is required) to counteract the offset slipstream trying to push the tail to the side.  It's usually 2 or 3 degrees to the left for an engine turning clockwise from the cockpit where the flow at the fin leading edge is coming from the left, or to the right for an engine that turns counterclockwise.
It's very common but not universal.  Some airplanes just use a fixed trim tab on the rudder to passively do the same thing, or both a tab and an offset fin.
They also often have the engine offset several degrees on the mount, to the right on a clockwise engine.  Look at single engine airplanes from above and it becomes quite apparent how the engine/prop is crooked as well as the fin being angled to the side, like the plane got into a fender bender accident and just drove off like that.  Makes you wonder how the dang things fly straight in the first place.

Some vertical stabilizers will have a slight angle of incidence to counter left turning tendencies. Older model Cessna 172s and 150/2s have a little metal trim tab that can only be adjusted by manually bending it from the outside. This will serve to adjust the vertical airfoil chord line angle in the aircraft slipstream or relative wind. The degree of incidence will be manufacturer and model specific.

I'm no expert, but Wikipedia helps. The angle of incidence is the angle between the chord line and a reference line on the fuselage. [source] Since the vertical stabiliser is on a different geometric plane, there can't be an angle of incidence as there is with the wings.

FYI, a vertical stabilizer has a chord line. It usually has not much of a net camber. But, it is not perfectly flat. A reference line would imply a 1 dimension aspect. The wings have an angle of incidence to a 2D plane on the aircraft represented by the ref line. The vert stab would have an AoI to a different plane represented by the same or a different ref line. The best ref line to use for both would probably be the longitudinal axis of the aircraft.


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At what point of the design process the manufactures build their first prototype?
I would like to know when the aircraft manufactures decide to put in practice their designs building the first scaled prototype (or maybe the actual size). Does the design have to accomplish a list of basic parameters or something like that?

There is no definite answer that will fit all manufacturers and projects for the question you're asking.
Simply put, the decision to create a scale model or a first prototype depends on what the goal of the creation is, the underlying technology, cost and market interest. A lot of aircraft, either new models or improved variants of already existing models never make it past the design stage. Other results in scale models to verify aspects of the underlying design or technology, while some may even skip this and go directly to a full-size prototype to be used for testing.
In some cases, a manufacturer will build a prototype regardless of market interest, because it allows them to showcase the technology and show that it actually works, while other manufacturers might not continue to that stage unless they have generated actual orders for the aircraft.
Needless to say these decisions will be based on different input from project to project, but generally speaking the end goal is to lower the risk if you decide to continue a project. If you are designing a very new aircraft, it makes sense to validate aspects of it before committing to production unless you can demonstrate that the risk is already low enough not to matter greatly.

Some might only prototype the cabin as well, to get a feel for how the interior will feel.

Absolutely. I don't have any data on it, but I suspect mockups are more common than scale model or functioning prototypes due to cost. Having a mockup allows you to showcase a new model using cheap materials that are easy to work with, and it also allows you to iterate and gradually improve a design without committing too much resources to a project.

Here's article on the Beech X700 mockup https://airfactsjournal.com/2018/04/beech-x700-the-starship-that-could-have-been/?trk_msg=JEU03RNQRTAKN0J09877JCL600&trk_contact=89220FV121KU2EPOOBPNU77O4O&trk_sid=8U594TMSK2DPJ6LQR651C5SOUS&utm_source=listrak&utm_medium=Email&utm_term=Beech+X700%3a+The+Starship+That+Could+Have+Been&utm_campaign=F20061A&utm_content=The+Magical+Mooney%e2%80%94New+From+Mac+McClellan  "the mockup of the X700 was destroyed and never saw the light of day"


text:
How do the vortex created by wing tips affects the lift?
I’ve been reading about how improve the aircraft performance and I found that for low aspect ratios, the vortex created by the wing tips decrease the lift generated by the wings. Why is this happening?

related if not a dupe: What is vortex lift?

I am not sure about the the duplicate: wingtip vortices are not the same as vortex lift.

In those post they talk about vortex and lift but, for me of course, @HiddenWindshield answered my question clearly

The lift over a wing comes from an imbalance of pressure above and below the wing. The higher the pressure, the more force is imparted to the wing. Thus, by generating a higher pressure on the bottom of the wing then on the top, a net upward force is created which offsets the pull of gravity on the airplane. The greater the pressure differential, the more lift is created.
At the end of the wing, there's nothing to prevent the higher pressure underneath from causing air to "spill over" the end of the wing into the lower pressure area. Thus, the pressure at the end of the wing tends to equalize itself, with a corresponding decrease in lift.

The result of equalize the pressure is the vortex, right?

@VicenteC Yes, as the air moves over the end of the wing from bottom to top, it's also moving from front to back due to the fact that the airplane is moving forward. It keeps spinning after it leaves the wing due to inertia, and that's the vortex.


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Logging time as SIC in part 91 and 135 ops
I am a holder of FAA and Argentinian Commercial ASEL,AMEL pilot licences. No type rating yet.
I am currently flying in Argentina for a company that owns several aircraft.  The two that concerns the questions are:
A B300 flew under part 91, and a B200 flew under part 135.
I am not yet in the annex as a designed pilot for the B200, being the sole manipulator at times, but I am already flying as SIC from the right seat.
For the B300 I am flying as SIC from the right seat, being the sole manipulator at times, there is no need to be in any annex since it's part 91.
The question is, how can I log this time
For the B200 (Part 135) as PIC under instruction on the empty legs? What about the legs with pax?
And For the B300 (Part 91)?

Are you flying under US rules or Argentinian rules?  It sounds like you are flying under U.S. rules.  Neither King Air variant requires a crew of two pilots.  You cannot log any time while the aircraft is operating under 135.  It is highly doubtful, you were a safety pilot under the Part 91 legs and so that time does not count either.

I am flying under Argentinian rules, but I was wondering how it would be in the US


text:
How is the Density Altitude performance penalty split between propeller and engine?
Let's say we have a Cessna 150 with a Continental O-240.
How is the density altitude performance hit split between the engine air intake and the propeller ability to "grab" the air.
Let's say I was able to put a engine on it that would not be affected by density altitude.
What would the remaining penalty be on the aircraft performance due to the propeller still being affected?

I don't claim to be an aerodynamics expert but this may be kind of broad. I think it would depend greatly on the length of a propeller and the volume of the engine cylinders. Generally, longer, wider propellers and larger engine cylinder volumes would be negatively affected more rapidly with decreases in density altitude.

There is no reciprocating gas engine or gas turbine which is not affected by density altitude, the density of the air directly affects how much mass of working fluid can be taken in by the engine for a given volume of air and as a consequence the amount of power it can develop for a given fuel consumption.  The less dense the air, the less power or thrust the engine can develop.
Turbocharging or supercharging a reciprocating engine can maintain uniform power outputs for a throttle input provided the density altitude does not exceed the critical altitude of the turbocharger.  Turboprop and turboshaft engine are generally 'flat-rated' ie the fuel controller maintains a uniform power output right up to the thermodynamic rating of the gas generator at altitude.
As for propellors, the thrust they can deliver is directly proportional to the density of the ambient air, so higher density altitudes mean less thrust for a given power input from the engine.
Performance tables for both engines and propellors are available from the manufacturer and vary between make and models.  In general, pilots really don't use this as much as the aircraft performance tables in the POH for a particular aircraft.


text:
Why do aircraft of the same model get progressively larger engines as they mature?
For example, the Cessna 172 started production with the Continental O-300 145hp engine but today sells with the IO-360. Granted that engine is more "modern" but 145hp with the O-300 still feels too little for such an airplane.
The Robinson R22 started with the O-320 and eventually jumped up to O-360.
Do the designers not feel the lack of power when test flying the aircraft? Are we getting fatter?

The Cessna 172 first flew in 1955.
The Continental IO-360 was FAA certified in 1962.
The math is pretty simple.
Yes, we (Americans, at least) are getting fatter, but that still doesn't allow for use of an engine that isn't yet certified.
It's the same for GA as well as commercial aviation. Improvements in fuel efficiency and power tend to lead the manufacturers to want to certify existing airframes for new power plants because that's less expensive (testing, certification, pilot training, etc.) than building a whole new aircraft around a new engine.

Older planes were simpler and lighter, in part to make certification easier and in part to minimize the selling price and therefore maximize volume.
Once that minimalist plane hits the market, though, customers invariably ask for things to be added, which nearly always means more weight. (Indeed, more weight itself is often the request, either payload or fuel, for airliners.) This means you will need a larger engine to maintain the same performance. And, of course, some customers will ask for more performance too, which means a bigger engine and more weight. It’s a vicious cycle that spins upward—and so does the price.
Such variations and advances are much easier to develop and certify once you have the certification and revenue stream from the minimalist model, though, so you can’t really skip that stage.

Increasing engine size allows improvements in performance. This can be used to open up new use models for the same or very similar airframe (putting 150HP in a piper cub, for example). It also supports practical use of seating capacity with full tanks in an existing airplane or safer operation at high & hot conditions or quicker climb outs, etc. All of these are valid selling points that make a given model of plane more attractive to a potential buyer. And if the buyer prefers the smaller engine for some reason, he or she can always buy the previous year's model on the used market.

Aaah, sweet memories. I added tail-dragger to my certification in a 65HP Cub. Two adults and take-off was like waitng for the curvature of the earth. Forward a few years and I did sailplane towing in a 180HP Super Cub -- that was a fun plane to fly single in (you had to do a few starts and landnings when not having towed for a while).

I think the idea "Cessna put bigger engines in the C-172 as bigger engines were certified" is a bit simplistic.
Compare an early model Skyhawk to a late model - they have very different empty weights, which is reflective of how the basic design got heavier over time.  Electric flaps, g-rated seats, seatbelts (and now airbags), more avionics, different wing shape, a vacuum system, big square dash, new landing gear - the newer ones are very different aircraft.  You can tell if you fly in them too, the older ones are not underpowered at all, if they're not overloaded.  A new 172 with G1000 weighs over 300lbs more empty than a 1956 model did, yet the 1956 model has a bigger useful load despite having 35 fewer HP.
Here is some data I pulled from the 1956 model handbook vs the S (G1000) model POH:
Model   Max Weight  Empty Wt    Useful Load HP  Wing Ld Climb   Takeoff Gnd Roll
1956    2,200.00    1290        910.00      145 13.8    660     1650    725
P/G1000 2,550.00    1663        887.00      180 14.7    729     1186    693

Takeoff distance is to 50', performance all assumes max gross wt. sea level, no wind, 15C.

I think it is especially important to look at the useful loads here.  If Cessna were upgrading the engine because "we're getting fatter" they would have increased the useful load.  Instead, the engines evolved over time - as did the airframe and equipment - as one cohesive design, while useful load stayed more or less the same (actually, it went down slightly).  It is a back and forth related to technology (1956 vs 2010!), and the additional engine power really is just enough to keep the design competitive (power to weight ratio on the 1957 model is 0.066 vs 0.0707 on the current model, which is part of why the distance over a 50' obstacle is so different, but the other numbers (ground roll, sea level climb) are fairly similar.).  In fact, I would suggest that an early 172 and a late-model both feel "underpowered" compared to a mid-70s N-model, when the design was still light but the engine made 160 HP.  With a power to weight ratio of 0.070 and a wing loading of 13.2, it climbs at 770 fpm at sea level, better than either of the other two.

I agree that there is more to it, but it is pretty simple that, in the specific example given by the OP, the engine he asks about could not have been installed at air frame launch because it wasn't FAA certified at that time. Were there other engines that produced that power they could have gone with? I dunno, but they didn't.

Sure, but they didn't need to.  I don't know what the engine market looked like in 1955 but if they'd wanted to put a 200HP engine I'm sure they could have.  They didn't because 145 produced the desired performance.  The 180 in 2020 produces very nearly the same performance, because the underlying aircraft is so different. It's kind of a chicken and egg problem. They couldn't really have made the engine smaller either.

In general, the smaller the engine the less challenging the initial development and the cheaper and sooner the new airframe will hit the marketplace.
Early adopters provide valuable feedback, while the sales force soon get to know what extras the market is most desperate for. Meanwhile engines are also evolving and market expectations advancing. The designer then better knows the weaknesses in the Mk.1 to fix, the strengths to exploit, and the engine powers to aim for.
Also, the low end of the market is most sensitive to price, while the higher end is most sensitive to performance. So it makes sense to  first launch down to a price with low performance, and then introduce the subsequent model with the latest and greatest engines.
For example when de Havilland specified the original ADC Cirrus for his forthcoming Moth biplane, the 70 hp Cirrus Moth was perfect for market expectations. Two years later he had made enough profit to develop his own Gipsy engine and the market now demanded nearer 100 hp in the Gipsy Moth.


text:
What is the maximum momentary G force that a modern airliner's wing can take before it snaps in extreme turbulence?
Taken from an aviation safety pdf..
Intensity - LIGHT - Vertical acceleration (g) 0.20-0.49 - Derived Gust (fpm) 300 -1,199
Intensity - MODERATE - Vertical acceleration (g) 0.50-0.99 - Derived Gust (fpm) 1,200-2,099
Intensity - SEVERE- Vertical acceleration (g) 0.1-1.99 - Derived Gust (fpm) 2,100-2,999
Intensity - EXTREME - Vertical acceleration (g) >2 - Derived Gust (fpm) >3,000
The g's in this list is additional g's. So ''> 2'' will read as 3 total g, as there is an additional g load factor of 2.
The limit turbulence load (the worst theoretical turbulence the plane  would encounter) for modern jets is 90-100 feet per second, or around  6,000 feet per minute. (FAR Continuous turbulence criteria):
''Uσref is the reference turbulence intensity that varies linearly with altitude from 90 fps (TAS) at sea level to 79 fps (TAS) at 24,000 feet and is then constant at 79 fps (TAS) up to the altitude of 60,000 feet.''
There is a 50% safety margin, so the max  turbulence it will encounter before a wing snaps off is about 150 fps.
What (momentary!) G loads would an airliner experience if it was  cruising and suddenly encountered a patch of 100 fps intensity  turbulence? (The ''worst case'' turbulence?)

I don't think an airliner's wings are going to snap off even in the worst turbulence. Boeing bent the 787 wing until the tips touched and they didn't break.

It's happened before, but with older models of aircraft. BOAC Flight 911. Braniff Flight 250, Wien Consolidated Airlines Flight 55, Widerøe Flight 933, NLM CityHopper Flight 431, BOAC Flight 783..

Can you provide a link to "aviation safety pdf" or other source information.

Each different aircraft model has unique features in how the wing has been designed & built. Each aircraft has its individual history of cycles, turbulence, hard landings, damage, repairs, and so forth. And, each encounter with turbulence, even "momentary", will be unique in terms of the G onset and drop-off.  There is no standard "momentary" of 1 to peak G in __ seconds, sustained for __, and dropping back to 1G in __. Put all that together, it's doubtful that there can ever be any single answer to the question in the title... an encounter one aircraft survives may induce failure in another.

Your title is disconnected from the question at the bottom.  Do you want to know the max G an airplane can take, or the G imposed by 100 fps?  The max G is something above 3.8, the ultimate limit for Transport Category, which can be considered a design minimum.  How much above will vary on numerous factors because there are fudge factors and "padding" to allow for aging/fatigue/corrosion and assembly flaws, maybe 4.5, maybe 6, so the answer is indefinite.

The G load depends on the speed. The vertical gust abruptly changes the angle of attack and the force depends on what lift the wing can generate. The weather penetration speed is such that the wing will stall before exceeding the (normal, not ultimate) structural limit.

His question assumes being above TAPS.  If I'm passing through some cells, I will slow to TAPS, but maybe I don't t think to do it, or you could encounter CAT without warning if there were no pireps or forecasts of CAT on the boundaries of a jet.

It's hard to give a direct answer to your question. But I will try to give a realistic answer.
As stated in the "Easy access rules for large aeroplane CS25" under EASA regulation:

Except as provided in sub-paragraphs (d) and (e) of this paragraph compliance with the
provisions of sub-paragraph (a) of this paragraph must be demonstrated in flight over the
acceleration range –
(1) –1g to 2·5 g; or
(2) 0 g to 2·0 g, and extrapolating by an acceptable method to – 1 g and 2·5 g

That's the normal range of load factors for a modern airline; of course an aircraft can be design to withstand more positive or negative G's, but most of them have an upper limit of +2.5g and -1.0g (in clean configuration), as stated in the regulation.
The following fundamental requirements have been developed around the experiences of metallic airframes and remain the basis for the certification of composite airframe structures. These require that the structure (by test and/or analysis) demonstrate the following capabilities:
• Static strength:
– Design limit load (DLL), no failure or unacceptable deformations. DLL is normally the maximum load anticipated to be placed on the structure in its lifetime. – Design ultimate load (DUL), no failure, although limited permanent deformation is acceptable; DUL = DLL × 1.5 (generally).
The limit of +2.5g and -1.0g will be our DDL, so if we "remove" the safety factor (1,5, but can be higher) the Max G load will be +3,75g and -1.5g. if you fly at this load factor the aircraft will not broke apart or will have catastrophic failures, but deformation can occur.
Let's talk about turbulence:
Extreme turbulence in reality is not part of the categorization of levels of turbulence (At least in EASA rules), the upper limit is the severe turbulence:

Turbulence that causes large, abrupt changes in altitude and/or attitude. Aircraft may be momentarily out of control. IAS fluctuates more than 25KT. (>1.0g at the aircraft’s centre of gravity)

So assuming a fluctuation of 1g (positive or negative) inside turbulence, we can assume that we will be able to reach +2.0g or -0g passing trough this turbulence.
If the turbulence will be "extreme" (let's assume a fluctuation of 2gs), we will reach a max positive G load of 3g and a negative G load of -1g.
As you can see, we still below DUL limit. I can tell you that probably the aircraft will not have any deformation in that range also if above DDL, this is because we are talking of instantaneous accelerations and not continuous and constant load factors (DUL and DLL are based on that).
The aircraft will however be checked after the encounter of severe turbulence.
Reassuming, is very hard that turbulence will cause any significant or severe damage to a modern aircraft. (Severe or Extreme)
But to give an answer to your question I can give you an example:
China Airlines flight 006 experienced vertical load factors of up to 5.1 g on 19 February 1985. The aircraft landed safely and there were no fatalities, but there was some damage:

From the NTSB incident report:

The wings were bent or set permanently 2 to 3 inches upward at the wingtips; however, the set was within the manufacturer's allowable tolerances. The left aileron's upper surface panel was broken and the trailing edge wedge was cracked in several places.

5.1Gs was probably the top of the load, but during the recover they were above DLL and DUL for a while.
This however didn't cause a catastrophic failure of the wing section.
I don't have any document or personal information or experience about the instantaneous or the continuous g Load to cause the snap of the wings, but I think that we are talking of +7/8g -4 continuous and +10-11g -5-6g instantaneous.
I hope that I answered your question.

The maximum load required for certification has to be maintained for three seconds if the test is successfully passed. You ask about momentary loads which is a whole different story. Wing bending will add inertial loads which reduce the stress in the structure and a sudden gust will not increase lift proportionally at once. It takes some time before air loads stabilize and a high frequency load will not uniformly stress the whole structure but will produce peaks and troughs. So it is impossible to give a firm number - the result will depend on a lot of incalculable factors.
Our understanding of atmospheric phenomena is quite well developed but it cannot be excluded that a "century gust" will overstress an airplane. The certification requirements aim to produce airplanes for which structural failure in normal operation is extremely unlikely and tests for strength using statistical models (where more intense gusts are less likely), but as with any statistics there might be an exceptional event which lies outside of those models. All we can say now is that this will be extremely unlikely.


text:
Why is the fatality rate in the Diamond DA40 so remarkably lower than the SR20/22?
I assume it has a lot to do with the stall characteristics, but with the SR20/22 having a combined 1.6/100,000 Fatal rate and the DA40 having .35/100,000 Fatal, it seems like a very stark difference. Additionally, the SR-- has a ballistic parachute and the DA40 does not.

Although they are new designs you aren't comparing like for like. The SR22 is a higher performance aircraft with 310hp as opposed to 180hp, and it has a longer range. It has more capability, which means it will be used differently.

Do we have a source for this statistics?

Not sure how true it is, but one theory I've heard about the high accident rate of the SR22 is the parachute. Every added safety feature tends to make people more careless. Was the same when airbags were first introduced in cars, accident rates shot up for a while before slowly trending down again.
Also, the DA40 is used more often as a trainer, while the SR22 is more often used by relatively inexperienced pilots who do have a license. Might well make a difference (student pilots tend to be more aware of the limits of their skill and knowledge than cocky fresh graduates who think that now that they are certified to know it all they really do know it all). And often that student will have an experienced instructor in the cockpit with him as well.

Also known as risk compensation/the Peltzman effect: https://en.wikipedia.org/wiki/Risk_compensation

Compared to other 180 hp airplanes the DA40 handles strong cross-winds better. It also has good visibility because the canopy bow is so far aft.
http://philip.greenspun.com/flying/diamond-da40
In defense of the SR20 what can be said is that the SR20 has a split-airfoil wing design that guarantees the wings will stall near the fuselage first, leaving the outer wings and ailerons unstalled. The result is very controllable performance right up to and including the stall.
http://philip.greenspun.com/flying/plastic-airplanes
That being said, a majority of accidents involving the DA40,SR20/22 or any  4-seat GA airplanes is almost always caused by Pilot error. So , it is not about the DA40 being more safe than the SR20. Splitting high and low fleet hours may result in too high a number. Ergo, the math is not precise.

It's true that most accidents are due to pilot error. But some aircraft may be more forgiving of errors than others. So even though technically it may be put down to pilot error, the difference may still be explained by design of the aircraft. We see similar results in light aircraft where Flight Design planes have a much higher accident rate than CubCrafters even though pilots in both cases tend to be experienced. It's mostly down to stall characteristics. There was a YouTube video on this from AVWeb.

Suggest you look at the design of the DA-40 vs the Cirrus aircraft.  Also compare the number of post-crash fires in each aircraft type (DA-40 has zero).  The Diamond's have dual spars in their wings, with fuel tanks between the spars (for crash protection).  The Diamond's also have robust fuel lines that resist pinching and breaking in the event of a crash.

@David, updated URL: https://www.diamondaircraft.com/en/private-pilots/safety/

@Peter - Thanks for updating., I deleted mine as it no longer worked.

If I had to place the blame on this one, it’s in the fact that the Cirrus aircraft are faster and more capable.  I suggest reading The Next Hour by Richard Collins about GA accidents and safety.  He talks at length about how faster, more aggressive airplanes tend to attract aggressive pilots who may lack the discipline to fly them properly or have extreme hubris in regards to their piloting abilities.  Add into this Cirrus’ somewhat deceptive marketing strategies where they seemingly tout the airplane as safe, almost to the point of invulnerable, with the CAPS system.  The general public’s and GA pilot pool’s ignorance of the capabilities and limitations of safety features combined with the high performance of the airplane as well as the large scope of private pilot privelages in terms of airplane performance also aggravates this.  This make for a situation ripe for accidents to happen.
To be fair the Cirrus SR20 and SR22 are excellent, docile and safe airplanes IF OPERATED PROPERLY.  And the SR20 has an excellent safety record, comparable with the DA40.  But the fly faster and operate faster in the pattern than does the Diamond.  And considering that 50% of GA accidents happen on approach and landing, at low altitudes at higher speeds with more impact energy where the chute is inefficitve as an escape system, it’s no wonder an SR-22 has a higher accident rate associated with it.

"And the SR20 has an excellent safety record, comparable with the DA40". This is not a fair statement. SR20 has about 3X the crash rate and over 5X the fatality rate. That is not what I someone would call comparable.

And where exactly are you obtaining this data from?

Actually current accident statistics indicate the SR20 had a fatal accident rate of 0.42/100,000 flight hours compared with the DA40 at 0.35/100,000 flight hours as of 2015.  This is probably due to much improved transition training on the part of Cirrus.  In the past the SR20 had much higher accident rates than the Diamond.

https://www.diamondaircraft.com/about-diamond/safety-features/ has the graph I was quoting but there are plenty other more independent ones with similar numbers. I've never seen the SR20 quoted that low. Is that just a single year quoted that low, or is this a consistent low over many years? Is it derived from the NTSB database like the other stats? Thanks!

FYI, another source with similar numbers: https://flygenesis.ca/flight-training-blog/why-diamond-aircraft-are-the-safest-choice-for-aviation-training/

I saw the Diamond site but the article referenced there made no mention of that info.

I had the same experience. I think that note references something further above the chart. Right above it, it references the NTSB database which is how I believe these charts were derived. It would have been nice if they had put date query stats next to it as well though.

authors: احمد الغرابي


text:
Why do older planes not have a middle hand luggage compartment?

Why do older planes not have a middle hand luggage compartment?
Where are the oxygen masks for the people in the middle rows?

L-1011 Interior:

777 Interior:

People back then had less crap they brought along

I would guess that there may also have been a bit more concern about MTOM on an L-1011 than a 777. i.e., less spare thrust, so less luggage allowed on.

There are two methods of doing the oxygen masks:

The well known ceiling installation.
A lesser-known seatback installation.

A safety card off an Ilyushin Il-86.
Searching for the relevant safety cards such as the one above should give you an idea which one was applicable.

I don't think this attempts to answer the question; it would make a better comment as the information is interesting and useful.

@JonathanWalters It does answer part of the question, where the O2 masks are located when not in the overhead.


text:
Is there a maximum lift to drag ratio?
If I recall correctly, the best competition gliders have a L/D ratio as high as 60:1. What imposes this limit? Is there a maximum theoretical L/D ratio, or could sufficiently advanced materials allow a glider with a L/D ratio of, say, 200:1?

@BenCrowell that may well be, but I don't think lighter-than-air craft count as gliders

@BenCrowell: Weight also goes up like third power.

@Jan Hudec nice to see some of your vintage commentary.  Surprised that it was not surmised that "weight" = (density x volume of aircraft) - (density x volume atmosphere) - lifting force generated from motion. Drag is friction from motion.  Buoyancy is insignificant for most aircraft, yet a pressurized cabin weighs a bit more at altitude.  Was trying to calculate ton miles per gallon for Graf Zeppelin.  Of course a motionless balloon has infinite lift to drag, but how much would it's volume effect drag once underway?

Yeah, balloons don't have drag, so why are we off on this tangent?  And are you talking about lift to drag ratio, or glide ratio?

With current technology the L/D might go up to 70 or 75, and going higher would require an almost impractically large wing span. Gliders need to fly in tight circles to use updrafts, and the larger the wingspan becomes, the bigger the speed difference between inner and outer wing will be. Also, landing such a wide wing without dropping a wingtip will be very hard. Smaller wings with a high aspect ratio will have a low chord length, leading to smaller Reynolds numbers, which translates into a steep increase of friction drag if the aspect ratio is increased without increasing wing area. Therefore, only adding wing span will help, and this runs into a soft wall beyond the 30 m of designs like the Eta. In addition, the current mass limit of 850 kg will make bigger aircraft unattractive for competition pilots.
The Concordia (pdf!) is claimed to have an L/D approaching 75, but I have learned over the years to see theoretical predictions as invariably optimistic, and realistic performance, with bugs on the wing and all, will never quite measure up to the hoped-for ideal.
Werner Pfenniger proposed to use boundary layer laminarisation by suction (pdf!) to reduce friction drag and proposed glider designs with L/D ratios in excess of 100. Turbines at the wingtips would drive the suction pumps, so these would still be unpowered aircraft. But so far nobody has dared to turn his visions into reality.
While laminarisation avoids the increase in friction drag of a turbulent boundary layer, a moving wall would eliminate viscous losses altogether. Now the friction generation is between the moving wall (this could be a taut foil running between two cylinders at the forward and aft end of the wing) and the fixed structure. With current materials there is no hope of reducing drag this way, but who knows what tricks will be possible in the future.
A glide ratio of 100 or more looks rather unlikely in the next 50 years.

Ah, I forgot that gliders have to circle updrafts.

Is there a theoretical limit though? Kind of like a speed-of-light for L/D?

@thepowerofnone     So what's the plan to eliminate skin friction?  I want to get rich.  :-)

That moving wall idea sounds cool! To be clear, this moving wall would have to somehow have to have the shape of the top half of the airfoil, right? And if you wanted to get rid of all friction drag you'd have to have a separate one on the bottom?

@raptortech97: Yes, correct on both counts. Ideally, the forward location of both cylinders should move with the angle of attack, such that the stagnation point is exactly between the two. Quite a challenge!

"Also, landing such a wide wing without dropping a wingtip will be very hard" - also, finding a suitable airport

@PeterKämpf do you have some literature or paper on the moving wall proposal, or did you come up with it yourself?

With any measure of aircraft performance, we must begin with the airfoil section.  All reasonable real-world airfoils start at about a 120:1 best L/D.  This is because with a testable airfoil you typically have an optimal combination of Cl = 1.2 & Cd = 0.10; hence the L/D of 120:1 (read "Abbott and Von Doenhoff" for more theoretical and practical considerations).
As you add the drag of extraneous components to your airplane like: cockpits, wheels, control surfaces, dirt, doors, screw heads, antennas, wing tips, ventilation, panel seams, and so on; you chip away at the best achievable configuration L/D.  For airplanes like the Space Shuttle you'll end up with a L/D of less then 5:1 (hence the phrase "Flying Brick").  A typical general aviation aircraft on the other hand, has about a 9:1 L/D.  For a sophisticated sailplane where extreme attention is made to the details, the configuration suffers only a 50% performance loss and achieves the aforementioned 60:1 L/D.  Higher performance is certainly possible, but is likely to be incremental in nature.
The starting point in designing an airplane often sets the initial configuration such that wing-skin friction drag is equal to the mathematical lift-induced drag.  Following that calculation, we start adjusting things until an acceptable configuration emerges.  The more realistic the first guess, the sooner the configuration emerges.
When evaluating advanced concepts like boundary layer suction or blowing, the performance cost of powering the air pumps is often ignored in testing; as is the reality that many microscopic pores quickly clog and are rendered ineffective, so be careful about taking the boundary layer control performance data at face value.

Welcome to Av.SE!

In your first paragraph, is that meant to read Cd=0.01, perhaps? otherwise the ratio is off by factor 10

Yes, you can have a L/D as high as you'd like. But I don't think you'd enjoy flying in milliKelvin liquid helium superfluid which has zero viscosity...

The lift and drag coefficient are defined with a fixed and uniformed pressure. Therefore, gravity and Archimedes' principle should not be involved in this topic. The maximum lift-drag-ratio is obtained with infinite wings. 2D airfoil optimization with genetic algorithm give the following optimization for the lift/drag ratio:
1/0.00166/0.002=300 000
https://optimization.mccormick.northwestern.edu/index.php/Wing_Shape_Optimization
This is a theoretical limit of course....which do not have some much sense in the present real world with finite wings, clear-air turbulence, surface roughness, water on wings,etc...

The 300000 is definitely the genetic algorithm exploiting a software bug or assumption.

Loosely speaking, L/D ratio is limited by the aspect ratio of the wing (its length to its chord width) and the friction of the wing surface (which is why frost/ice on the wing is a bad thing -- it dramatically increases wing friction).


text:
Why does the FAA have a daily DOF and another that's only updated every 56 days?
The FAA has a Digital Obstacle File (DOF) which reports on tall objects that would be important for pilots which is updated every 56 days.  https://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/dof/
They also have a Daily DOF which purports to do the same thing but is updated daily.  https://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/dailydof/
Why have both?

There’s very different use cases for the information.
If I am putting up a 200 foot meteorology tower in a city, this is of no concern to commercial, military, or general aviation operators.  So it will be placed in the DOF right away, but since it doesn’t affect flight in the normal IFR or VFR environment, it doesn’t have to be propagated to all pilots right away.  But there may be some special operators--mosquito spraying, ag application, etc.--that may want to check the DOF before a specific sortie, so the daily is available for them.  Organizations that work with this data to create, or consume this data can get a an "OE/AAA" online account.
A taller tower that penetrates routine use airspace or even a shorter tower that approaches the obstacle clearance gradient near an airport is another story completely.  In these cases, the proposed tower is coordinated with the FAA OEG (Obstruction Evaluation Group) and goes through a process called OE/AAA.  The obstruction goes through an analysis because VFR charts and instrument procedures all need to be updated.  Oddly, the notice required by the FAA is only 45 days before start of construction, so they're assuming it will take you a few weeks to penetrate airspace.  If needed, new obstacles that do penetrate airspace and are not yet charted will be addressed by NOTAM.
Also, any tower over 2,000 feet AGL falls in a different category.  Below 2,000 feet you are primarily "coordinating" with the FAA.
But anything over 2,000 feet is considered a "potentially inefficient use of airspace" which triggers a required approval process by the FAA, similar to an impact statement.  There are no buildings over 1,500' in the US, 20 radio towers exactly at 2,000', and only 4 taller;  so this isn't a call the FAA gets often.
The FAR that covers this is Part 77.  14 CFR 77.9 states:
Any person/organization who intends to sponsor any of the following construction or alterations must notify the Administrator of the FAA:

Any construction or alteration exceeding 200 ft above ground level
Any construction or alteration

within 20,000 ft of a public use or military airport which exceeds a 100:1 surface from any point on the runway of each airport with at least one runway more than 3,200 ft.
within 10,000 ft of a public use or military airport which exceeds a 50:1 surface from any point on the runway of each airport with its longest runway no more than 3,200 ft.
within 5,000 ft of a public use heliport which exceeds a 25:1 surface

Any highway, railroad or other traverse way whose prescribed adjusted height would exceed that above noted standards
When requested by the FAA
Any construction or alteration located on a public use airport or heliport regardless of height or location

As is often the case on Stack Exchange, you  now officially have too much information.

I don't really see there are 2 different use cases.  I can see why someone might not care to get the new daily file everyday but why would anyone forego the previous day's daily file to get the file that could be up to 56 days old?

@DeanMacGregor Remember that these files are not intended for use in flight planning.  Published and NOTAMs are authoritative, and in Parts 91, 121, 135, etc we are required to fly using them.   We may find the DOF data interesting but we are not the intended audience.  There are very foreseeable cases where a data consumer needs the exact DOF version that corresponds to an exact version of published charts they are using, so they want to be able to download the file upon which those charts were based.  (cont...)

(...cont)  But 99% of the time, we're not supposed to be doing anything with the DDOFs, we're supposed to be using NOTAMs, the only approved way for us to consume the information.  You see the 56 day file as being "outdated" but many use cases see it as "matching the current charting."  Part 77 requires the files to be made public, and so they are posted to a website, but that does not mean that aviation operators are the intended audience for those files.

The 56 day file is used to update charts and published procedures (which are also on a 28/56 day cycle). Obstacles that are not yet incorporated in the 56day publications must get a NOTAM.
It is one database. The two object files are snapshots. There are also change lists for each. The change lists contain additions, removals, and updates to accuracy since the last snapshot(one day or 8 weeks of change). The 56day file and 56day change list are particularly useful to keep the many teams in many locations around the country working on many products all synchronized and avoid mistakes with exactly which day's data is being used and which data [changes] need special attention.

So does the daily update ONLY contain obstacles that are NOT listed in the 56 day?

@MichaelHall It is one database the two object files are snapshots.

I was curious myself, so I actually asked the FAA.  This is the response I received:

I received your inquiry asking about the difference between the DOF (Digital Obstacle File) and the DDOF (Daily Digital Obstacle File).  You are correct that the two products provide generally the same data, one on a daily basis, the other every 56 days.  Due to the fact that our stakeholders have a variety of needs, where some need that data to match other products, such as charting, which provides updates on a 56 day cycle, while others need the data changes much more frequently, the two products may have entirely different users for much different reasons.  We want to provide the obstacle data for those stakeholders who have different needs.
I hope this makes sense and provides you with an explanation for the similar but very different products and their uses.  Should you have any other questions, please don't hesitate to contact me.

Personally I find "generally the same" and "similar" to be completely unhelpful.  It would make perfect sense to supplement a 56 day database with a daily update of what has changed since the last release, but if the daily data includes ALL obstacles there is really no need for the 56.  Just go get the latest daily data whenever you want an update.

Thanks for reaching out to them!  As was mentioned in their response, “some need that data to match other products, such as charting…”  I mentioned this in my answer as well.  Remember that the use case for these files is not pilots but people that are correlating data for various uses.  Over the years I have downloaded DOF files maybe 5-ish times, and in each of these projects, it was important that I had the data that matched the currently released charts and procedures exactly.  Most of the use cases others have for the data I am aware of are similar and require the 56 day DOFs.


text:
Is it possible to calculate lateral acceleration from pitch/yaw/roll rates?
Can you calculate an aircraft's lateral acceleration from the aircraft's yaw, pitch and roll rates? If so, how?
This is to implement a digital slip indicator.

I'm confused. You want to measure lateral acceleration or sideslip? Lateral acceleration can be simply measured by accelerometers, they are cheap enough.

No. Yaw, pitch and roll rates only describe the change in the orientation or attitude of the object relative to a frame of reference. Is it changing orientation to point further clockwise? or counter clockwise, or upwards/downwards, etc.
Any acceleration is a measure of the change in the velocity of the object relative to the frame of reference in question. An object can be rotating to change it's orientation or attitude in any way completely independently of it's velocity through that frame of reference or how that velocity might be changing.

No. You can have lateral acceleration with no change in attitude, and thus no yaw, pitch, or roll rates. An example would be a change in the crosswind. If all you have is attitude (i.e. yaw, pitch, and roll angles, with or without their rates), you don't know translational acceleration.

Yes, but only if you know the aircraft's airspeed and orientation in space, and the rate of change of the slip angle and angle-of-attack.  After subtracting these last two variables from the yaw, pitch, and roll rates, the residual values must come from actual changes in the direction of the flight path, and if you know the airspeed, then you know all the accelerations involved in these changes.

Cool, but why not use GPS or radar? The OP didn't ask "...from angular rates and whatever else you want" ;)


text:
Can APU start in-flight using RAT or battery power?
Is it possible for a passenger jet to start its APU using power from the RAT? If so, are there plausible benefits to doing so (like supplying hydraulic pressure to the wheel brakes)? Do modern passenger jets frequently (ever?) operate with the APU not running?

On the 737, the APU is typically started from battery power; this is normally done on the ground, but it could be started this way in flight as well.  (The 737 doesn't have a RAT.)  The APU is typically operated only on the ground for short-haul flights, although there are cases such as a generator that failed in flight when it's started & used in the air.  It's also used in cases of a "bleeds off takeoff" to provide air conditioning and pressurization when the engines aren't supplying bleed air (to increase power for a hot, high, and/or heavy takeoff).
But yes, it's more common than not for modern passenger jets to fly with the APU off on moderately short legs.
The exception to this is that some jets are required to run the APU during long over-water (ETOPS) legs, so that if one generator fails, the APU's generator is available without the question of "will the APU start after having been cold-soaked at altitude for so long?"  So in that case running it for much of the flight is common.
As far as the APU vs a RAT, the APU is almost always going to be a bigger generator than a RAT, so it can power more electrical systems on the aircraft than a RAT.  These would probably include electric-motor driven hydraulic pumps, which again will probably have more capacity to provide hydraulic power to flight controls & other things than a RAT would alone.  Plus, an APU can provide pneumatic power (bleed air, i.e. pressurization) than a RAT can't.  The other side of that coin is, a RAT is typically able to produce power more immediately after it's called on than an APU, which takes some tens of seconds to start up.


text:
How do airports detect drones?
Recently, there's been a lot of coverage in the news of drones disturbing operations at airports.
Do airports have a method to detect drones? If yes, how does it work? If it's still an emerging technology, is it something being looked into?

The number of drone sightings near airports is increasing (apart from last year), and frequently this results in temporary interruption of operations at airports, with enormous economic consequences. Most famous example is the December 2018 drone incident at Gatwick  which affected the airport operations for more than one day.

source: EASA Drone Incident Management at Aerodromes(pdf)
I live in Germany, where there have been over 500 sightings near airports since 2015, including several high-impact cases that resulted in the interruption of air traffic at major airports such as Frankfurt airport. Last year, the German Air Traffic Control (DFS) tested a number of drone detection systems  (press release, video link, article in German)  at Frankfurt and Munich airport as part of a market evaluation. Over 600 drone flights were performed, at distances up to 10 NM from the airport. I was involved in the design and execution of those tests and I can share a few observations.
At most airports in the world, drone detection still primarily relies on humans that happen to see a drone fly and inform the police, airport security or control tower by phone or radio.  There are a number of severe limitations to that approach, for example:

Drones are typically small and difficult to see at distances of more than 100 meters. At the scale of a major airport, it is plausible that drones can fly in safety critical areas for a prolonged time without being seen.
Position reporting to those that need to act upon the information (air traffic control, police, security staff) is delayed (phone call, relay of info) and inaccurate ("near the terminal", while the terminal building stretches over more than a kilometre).
Independent verification of the reports is difficult. This opens up the possibility to falsely report drones in an attempt to shutdown the airport.

To address these limitations, drone detection systems are under development, and some airports have deployed them with varying levels of success.
Ideally, a Drone Detection System (DDS) meets these high level requirements:

it detects all drones in the vicinity of the airport
it locates these drone(s) accurately
it does so without delay
it has a very low false alert rate (preferably no false alarms are raised at all)
it locates the position of the remote control (not needed for safety of air traffic, but helps the police in finding the drone pilot)
it does not interfere with aviation communication, navigation and surveillance systems.
preferably the system does not need any supervision; having staff 24/7 dedicated to drone detection is very expensive.

There are many drone detection systems available in the market, at various levels of maturity and some more suitable for airport use than others.  Most, if not all drone detection systems, make use of various sensor types.
There are four categories of drone detection sensors:

Optical / infrared cameras
Radars
Radio detection systems
Acoustic detection systems

Optical / Infrared cameras
One way to detect drones is by cameras. But at the size of a major airport, you are almost always far away from the drone. This means that the camera must be able to zoom, zoom a lot. Some of the best cameras are able to show a clear picture of a 40 cm size drone at 2 kilometres, and a recognisable dot (distinguishable from birds) at several kilometres more. The problem is that with such zoom levels you have a very narrow field of view and so you are never going to detect a drone that you didn't know about before. Therefore cameras are not a good choice as primary sensor, they need to be pointed in the right direction by another sensor.
Once they are pointed at the object of interest, image recognition is often able to classify the object as drone or something else. Some camera systems do a great job optically tracking moving drones, others need manual input.
There are systems that use the camera subsystem for locating the drone, by combining the view angle of several cameras to calculate where the lines-of-sight cross. Laser range finders can also be used in combination with cameras to determine the distance of objects from the camera. Other systems just use the camera as means of classification of an unknown object, not for determining the position.
Having a combination of Infrared (IR) and visible light is beneficial. For one, because at night there is not enough visible light to see the drone, but also the contrast of the drone against the background is often much better in IR than in visible light.
Radars
Radars are an obvious choice of detecting flying objects near the airport. Unfortunately, air traffic control radars and surface movement radars are not able to detect objects of the size of a drone.
There are dedicated drone detection radars on the market, some with a background in military, border control or bird tracking, that are specifically tuned for drones. The maximum distance at which these radars detect a drone of course depends on the size of the drone, but also its shape and the manoeuvring it is doing. There are significant performance differences between radars, and even a good radar may perform badly if it is not properly tuned or sited.
Since these radars have to be very sensitive to pick up a radio reflection from a drone, they see almost everything: planes, cars, cyclists, birds, wildlife, trees moving in the wind etc. One of the biggest challenges for drone detection radars is to distinguish drones from other objects.
False alarms need to be balance with missed detections, which is a delicate process. In the end, a radar will occasionally classify something as drone while it is actually something else.
Radars transmit radio waves that potentially interfere with CNS systems at the airport. Most systems I have seen were operating at frequencies far away from aviation systems, and those that were operating at similar frequencies did not cause interference. (After doing a paper analysis first, the systems were switched on to see if there was interference. This was done at night when air traffic levels were low, and with all relevant people made aware before the system was powered up)
Radio detection
Radio detection systems work by detecting the radio signals transmitted by the drone or their remote control. These systems contain a library of signal properties and they recognise which signals belong to drones. Most systems I have seen cover vast frequency ranges.
The location of the drone (or its remote control) can be found by triangulation or multilateration. Some systems can decode data packages from specific drone models and read the GPS location directly from the drone and the remote control.
Since there are many radio signals transmitted at the airport, the background radio noise is quite high. Also radio signals reflect of large buildings such as hangars and terminals. This has an effect on the performance of radio detection systems. Some systems are severely impacted by the airport environment while other systems are less affected.
Of course these sensors only work if the drone transmits a signal, does so on a supported frequency, and with a protocol known in to the signal library. None of the systems I've seen was able to detect all drones in the test.
Acoustic
Finally there are acoustic detection and location systems, operating in the acoustic frequencies band.
These are passive systems that rely on detecting the noise characteristics of drones (specifically their propellers). They have a very limited range (up to ± 300 m) and are  susceptible to background noise, which degrades their performance.
Due to these characteristics the use of acoustic detection systems in airport environments is very limited. If there is any use at all, they could perhaps be used as a coverage gap-filler, for example between hangars.

A good drone detection system will make use of various sensors types and integrate their outputs using a multi-sensor data fusion and tracking system to a single, reliable situation picture. In every class of sensors there are some really promising products, but a  strong integration of a range of good sensors is hard to find. This market is developing quickly and I expect that the situation will be very different in a few years.

Another issue with radio detection is that drone signal is indistinguishable from Wifi or Bluetooth so anyone (passenger, pilots, ground crew) with a phone would also be detected as a drone

@slebetman, that is not the case.

Is there a potential for the radar detection in wavelengths that can detect drones to interfere with weather radar?

@TomMcW There's potential for any radio source to interfere with any radio receiver. But, given how long radar has existed, I think it's pretty safe to say that we've got a handle on how to keep different radars from interfering with each other.

@TomMcW There is definitely a possibility of interfere with airborne and ground based weather radar, as well as surface movement radar. A number of systems operate in the 9 GHz band. However, careful frequency management and differences in signal modulation combined with modern signal processing technologies can prevent interference problems. Hence the paper exercise before switching things on.

You may also add passive radar using FM and DVB bands illumination.

@mins, indeed that should be added. I left it out because there are to my knowledge no systems available on the market that use passive radar for drone detection.

@mins And thank you for the bonuses. Very kind of you! I much appreciate the gesture.

There are already a few: Hensoldt TwInvis, Patria Muscl and Indra is developing one too.


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Does the A320 Trimmable Horizontal Stabilizer automatically reset after landing?
Does the A320's Trimmable Horizontal Stabilizer (THS) automatically reset after landing? If so, is there any condition where it doesn't? And what about the rudder trim?
I'm asking because I'm studying from an old FCOM I found online and it doesn't state that any of those automatically reset but there are two questions in SmartCockpit that say otherwise (i.e. that both the THS and rudder trim reset after landing).

THS - Trimmable Horizontal Stabilizer


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Could a flight engineer fly a jet solo?
In modern two-engine planes, if one pilot is disabled, it's my understanding that the remaining pilot can safely fly and land the plane. But what about in aircraft like the 727, which had two pilots and a flight engineer? Assuming the FE had flight training, could they land the plane if the two pilots up front were incapacitated? More generally, what is the minimum number of pilots required to safely land a jet with a three-person cockpit?

You've asked a question the answer to which is in large part a matter of opinion. Also, which three-person cockpit aircraft you're talking about also enters in, as does the stage of flight, as do the conditions at the airport of intended landing. All this, in my opinion, means the answer is "maybe" insofar as an FE who had had flight training be able to get the airplane down safely, and the currency of the FEs piloting would be important as well.
As far as the minimum number of pilots required to safely land a jet with a three-person cockpit (a separate question really), one pilot and the FE can safely land the airplane. In a normal landing, the flying pilot is doing most of the pilot work. The non-flying pilot typically is doing the radio work and manipulating the gear and flap levers at the command of the flying pilot. Since pilots usually trade legs, both are used to doing all that needs to be done. If a non-flying pilot is not there, the flying pilot can easily reach the flap and gear controls, and he's used to manipulating them when acting as the non-flying pilot.
In the scenario of an FE leaving his seat and sitting in a pilot seat and performing the piloting, there is the problem that the FE panel generally cannot be reached from a pilot seat. To a degree, depending on the stage of flight, the FE could pre-set his panel for the landing.
Some years ago I wrote a novel (unpublished) in which I had a single pilot fly a 747. In the novel the pilot had fashioned a wooden pole long enough to reach the FE panel from the captain's seat. The pole had at one end an arrangement that allowed the pilot of manipulate the necessary switches and dials on the FE panel.

So if a FE had become incapacitated on a 747-100,-200 would one of the two pilots have to go back and man his station?

@TomMcW My solution to that scenario would be to first decide which pilot could best run the FE panel, and have him go back to the FE seat. The FE seat both rotates and slides forward and aft. For takeoff and landing, the seat is rotated to face forward and slid all the way forward. From that position, the FE can manipulate the thrust levers, the flap and gear levers (with a little stretch for the gear). Thus whomever is in the seat can easily perform the non-flying pilot duties. In cruise, the FE's work is intermittent, so you could move between a pilot seat and the FE seat.

@Terry How qualified are pilots at running the normal FE work? I have no idea how qualifications work in three-person cockpits!

@gsnedders That's a separate question well worth asking in my opinion as a regular question. It's also one that to properly answer will greatly exceed the character limit of comments. So, if you post a question, "How able were pilots of three-man cockpits at running the normal FE work?" or some such, I'll be happy to answer.

@Terry Sure, didn't know how long the answer would be! Question is here.

When's the novel going to be published? If it's anything like your answers on here, I'll be the first to buy a copy!

@DavidGlickman Thank you for the kind words. It's highly unlikely to ever be published, but if you go to http://terryliittschwager.com/novel.php, you can read it online.

Floyd J. Stelly points out that National Airlines, at least, required FE applicants to have jet pilot ratings.


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Why do Airbus A220s manufactured in Mobile, AL have Canadian test registrations?
I noticed that there are occasionally test flights by Airbus A220 aircraft in and out of the Airbus production site at Mobile, Alabama (KMOB). Some of these aircraft use what are presumably test registrations for the flights, but these test registrations are Canadian. Here is one such flight, using registration C-GPUV. I know the A220 was originally the C-Series, produced exclusively in Montreal by Bombardier, a Canadian company, but shouldn't the aircraft produced in the US use US test registrations?

shouldn't the aircraft produced in the US use US test registrations? I don't think this premise stands up. An aircraft can be registered anywhere, to suit its owners effectively. Lots of people register their aircraft according to the legal regime they want to operate under. I.e., I presume Airbus want to align to Canadian regulations

The airplanes are built/owned by an Airbus subsidiary incorporated in Canada, and the Mirabel facility is still the primary production facility and location for the engineering organization, etc.
Mobile is effectively a "branch plant".
It's still a Canadian certificated design, being built by a Canadian incorporated business entity (an AB subsidiary), with Transport Canada as the primary regulator for all certification matters. Therefore, aircraft have Canadian Registration before a C of A is issued.

The various certification organizations have reciprocity agreements.  When the FAA certifies an aircraft, Europe, Canada, Australia, etc. accept that certification.  That way, Boeing (for example) doesn't have to go through cert multiple times in different countries when it wants to sell to different customers, or those customers want to operate in different countries.
Not all countries have the capability to certificate an aircraft a the highest standard.  It takes a large investment to get to that point.
The A220 was a Bombardier made CSeries that went through cert in Canada.  It would be terribly expensive to re-certificate an aircraft just because you built a new factory in a different country.
Furthermore, you are not limited to the manufacturer's country of origin for the initial cert.  For example Bell Helicopter (Textron) from Ft. Worth Texas often certificates helicopters in Canada.
Here is a list of bilateral agreements from the FAA.  These agreements do not have to be symmetrical -- i.e. Country A may accept cert from Country B, but not vis-versa.

As a side note, Bell Helicopter Textron has facilities in Mirabel. Not very far from Airbus, if I'm not mistaken.

Yes, I believe that is a maintenance and training facility that they also use as a home base for cert and some other things.  Their HQ and primary engineering design team is in Ft. Worth.

I thought they also designed and built some in Mirabel, but I may be mistaken. We regularly heard about the company in the years after they set shop there, but it's been a long time since I heard anything. Could be that their role changed over time, too.

Hard to tell.  It does appear that most Bell commercial helicopters are assembled and delivered in Mirabel.


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What are those structures at Taif Regional Airport in Saudi Arabia?
I was looking at airports in Saudi Arabia and noticed a strange one. At Taif Regional Airport near Mecca there are a bunch of taxiways all seemingly randomly intersecting at different angles, each with a bulge in their width and a structure built in the middle of the bulge. Based on the shadows, they seem to be sunken by some amount with the structure built to roughly the same height that the taxiway is sunk. I counted at least 30 of these structures. The measuring tool on Google maps shows them to all be around 135 feet wide, and of various lengths.
I couldn't find any information about these structures or their purpose. Are they hangars of some sort? If so, why the strange design?


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How dangerous would it be to start a jet engine with coins inside?
With the multiple stories in the news of people throwing coins into a jet engine for good luck, I couldn't help but wonder how dangerous it would be if the act went unnoticed and the crew started up the engine with the coins inside. Would the engine be damaged? Would the damage be noticed before the plane throttled up for takeoff or left the ground? I'm sure the answer is, to some extent, "it depends", but what's a worst case?

this question should be a duplicate of "how dangerous if rock sucked in"

I guess it works - it was "lucky" that other people noticed before the engines were fired up, thus eliminating potential for damage.

As you say "it depends". Modern jet engine front turbines are designed to reject foreign object debris outside the core, which is where the damage would really matter. Jets suck up hard foreign object debris like pebbles often enough and it will ding things a but but hardly cause catastrophic damage. I'm sure coin throwing has gone unnoticed, and it made no difference in the end.
Really, it's not a big risk for the most part, modern high-bypass turbofans have a large bypass duct, when coins are thrown into an engine which is not running they will drop to the bottom of the bypass duct and get blown harmlessly out the back when it's started. However, there's just enough risk that a coin could find its way into the compressors and cause enough damage to need expensive repairs, and that is why they will take the airplane out of service.
Of course it depends on the coin, if you threw this bad boy in it would be a different story:

Well, if tossing something like that in went unnoticed, I'd be more worried about the competence of the crew than the reliability of the engine. Seriously, though, I imagine with a (regular-sized) coin, it would get pushed out of the engine quite quickly one way or the other, right?

If someone tosses a coin in the engine while it is stopped it will almost certainly get blown harmlessly through the bypass duct when the engine starts up. If the engine is running it will still probably go through the bypass.

A thrown coin going in an arc @AnandS, it would be tough. I imagine it's within the realm of possibility.


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Why is one of Madera Municipal's runways labelled with only "R" on both sides?
I was looking on Google Maps satellite view and noticed Madera Municipal Airport in Madera, CA (ICAO KMAE) has an east-west runway labelled with nothing but the letter "R" on both sides. There is no parallel runway. Why the strange marking? Airnav reports it as runway 8/26, so why not label it that?

Composite for both ends via Google Earth

Visible in the foreground: The ISS

An operation I am familiar with uses a turf runway, not listed in the AFD, which is parallel to a paved runway for their ag operations.  Time is essential when reloading ag operators, and the turf runway accomplishes that.  When conditions dictate, they may use the paved runway, but turf is preferred.  Waiting for students to run up a C150 several times a day has a direct impact on productivity.
Similarly, another field has a turf runway parallel to a paved runway, which is used for a glider club.  It speeds their operations, and is safer for them, and less aggravation to the folks using the paved runway.  IMO there could be better signage to explain things to transients, but as a sometimes tow pilot for them, it does simplify things quite a bit, and the ropes last longer on grass.
Finally, the first airport mentioned also had glider operations at one time on the other side of the paved runway, which resulted in traffic advisories such as XXX LANDING ON 28 RIGHT TURF, and XXX LANDING ON 28 LEFT TURF.  Again, it caused some confusion, but greatly enhanced the airport's capacity, and had a relative increase in risk reduction by  a small separation of differing traffic close to the thresholds.

Cool! Thanks for that info, clears up why an airfield might have a dedicated runway just for ag (or glider) use.


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Why is the font size of runway numbers in Canada small?
I've noticed that on runways at Canadian airports, runway numbers are painted noticeably smaller than runway numbers at airports pretty much anywhere else. For instance, here's the beginning of runway 32 at Ottawa Airport in Canada, and here's the beginning of runway 32 at Buffalo Airport in New York. Or the beginning of runway 32 (left) at Madrid airport in Spain.
Does anyone know why the runway numbers are printed smaller? Wouldn't it be best for them to be nice and large so as to be readable from the air?

After reading @ymb1 answer, it is strange that FAA (among other) didn't adopt ICAO size, but doesn't declare the deviation in the US AIP. The deviation from §5.2.2.6 in Annex 14 of Chicago Convention should be mentioned the way it is done for, e.g. §5.2.2.4: "Zeros are not used to precede single digit runway markings" (see page GEN 1.7-86 of the AIP).

@mins That's odd. I could swear I've seen "09" painted on US runways. Am I nuts or did they change at some point?

@TomMcW: It was already mentioned in 2009 AIP. I can't find older versions.


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What is this radial-engined US Navy aircraft in Iceland?
My parents are traveling in Iceland and sent me a few pictures of an old radial-engined aircraft. It has "United States Navy" markings on the side, "Keflavik 17131" on the tail, and "191" on the nose. There's a picture of one wing with two engines, so I assume it's got four total. Unfortunately I don't have an exact location, except that it's in Iceland.
I'd love to know what this is, but perhaps also how it might have ended up abandoned by the Navy in Iceland.

It appears to be a Douglas C-117 which is a C-47 with more powerful engines. Tail number 17191 flew out of Iceland
https://www.airliners.net/photo/USA-Navy/Douglas-C-117D-DC-3S/2157319
From the linked website:

Standing in front of the weather office, 17191 is ready for another flight to one of the radar stations around Iceland.

The aircraft has the same KEFLAVIK and tail number markings

Ok, I understand now. Based on the third and fourth pictures I thought it had four engines, but now I see that the fuselage attached between the two engines. Any idea what the aircraft is doing there in Iceland?

@AshleyStrout It was probably based there. The US had a military base in Iceland until 2006 (NAS Keflavik).

Sad to see a once beautiful plane like this, abandoned and crumbling to a pile of garbage. Also makes me feel old--it looks like it's been abandoned almost forever, but I can remember 1976 (when the picture was taken) quite clearly...

@Jerry Coffin when I hear stories of crazy rich people buying half million dollar yachts I think "why wouldn't you buy one of these planes and restore it instead!?" It would be a cool plans to arrive anywhere, especially in the classic livery.

That’s a Douglas R4D, the Navy version of the C-47/DC-3.

Can you add some sources to your answer please?  As it currently is, your answer is at risk of being deleted.

Unfortunately I can’t. I just know what the DC-3 looks like, and being a Navy aircraft, I can extrapolate that it is, indeed, an R4D.

It was built as a C-47A-20-DK Skytrain 42-93105 (MSN 12980) for the USAAF Apr 12, 1944, then transferred to US Navy as R4D-5 BuNo 17191 Apr 12, 1944, and then later redesignated as C-117D. https://flydc3.de/planes/detail/265/

17191 (MSN 12980) ex USAAF 42-93105. To US Navy 12Apr44. NATS 12Apr44. VR-3 Aug44. VR-9 22Dec44. VR-1 Feb45. VR-7 Apr45. VR-3 Aug45. Jacksonville May46. NART Glenview May46. Converted to R4D-8 with new MSN 43379, returned to USN from Douglas December 1952. Europe Jun59 to 18Sep62. To C-117D 18Sep62. Europe 18Sep62 to Dec70. Mildenhall 1971 to Oct73. WFU. Retired from service 1973; in 1987 was on display at NAF Keflavik, Iceland. Moved Sept 2002 to Egils Olafssonair Minja-Og Fugminjasafn at Bjargtangar, Iceland. http://www.joebaugher.com/navy_serials/thirdseries2.html

Bonjour, le C-117 est la dernière version (R4D8) du mythique DC3. Outre les moteurs plus puissants (1450 ou 1475 ch au lieu de 1200), il est "nouveau" à hauteur de 75% des pièces, même si la ressembalnce avec le C47 reste frappante. Fuselage plus long, queue "genre DC4", nouveaux panneaux extérieurs d'ailes,, train totalement caréné sont les principales différences. Gros échec commercial, les 101 avions construits (la plupart par transformation de DC3) sont des raretés pour lesquelles un musée donnerait une fortune. Voir ce C-117 pourrir est une honte.

Translation using Google Translate -

Hello, the C-117 is the latest version (R4D8) of the legendary DC3. In addition to the more powerful engines (1450 or 1475 hp instead of 1200), it is "new" up to 75% of the parts, even if the resemblance with the C47 remains striking. Longer fuselage, "DC4-like" tail, new outer wing panels, fully faired undercarriage are the main differences. A big commercial failure, the 101 planes built (most by DC3 transformation) are rarities for which a museum would give a fortune. Seeing that C-117 rot is a shame.

Welcome to Aviation.se Sorry, but this is an English community. Could you translate your post? Otherwise it will have to be removed. Thank you.

@Federico I actually happen to know French - am I allowed to submit an edit request with a translation?

@AshleyStrout theoretically you could. the problem is that it would be hard to verify that the translation is accurate. and the user probably won't learn about the requirement to post in English.

@AshleyStrout please verify the accuracy of the translation that has been provided.

@ThomasPerry looks good to me!

It's an R4D, a Naval version of the Douglas C-47/DC-3.


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Can TS-1 fuel be used in an aircraft that takes Jet A?
Reading up on some airports in Russia I noticed that some only supply TS-1 jet fuel (see point 7) instead of Jet A. I tried to find out more about this fuel, but only saw that it has a lower freezing point and a higher flash point. What I couldn't figure out was if this fuel is "compatible" with Jet A. Could a plane that usually flies with Jet A operate with TS-1 instead, or vice versa? My guess is yes, but I couldn't find anything authoritative about this.

I'm still looking for same answer as well, even AFM (Fuel System Limitations) not enough details regarding TS-1 fuel

The answer is maybe.  You would have to check the Fuel System Limitations in the Operating Limitations in the AFM of the aircraft in question to find a table or list of the approved fuel types, which may or may not include TS-1, and if it doesn't you're kind of stuck.
For example, if I look up the allowable fuel grades for the CRJ700, it includes several worldwide standards (American, British, Chinese, NATO etc), and a fuel type is listed as "RT" under CIS (Russia's official name - Commonwealth of Independent States I believe).  But there is no listing for TS-1, so unless RT and TS-1 are the same thing and you have official documentation confirming that, it can't be used in the RJ (I'm retired and the pilot reference handbook I'm using is quite old and out of date so perhaps TS-1 is listed in current ones, but in any case you get the drift).
You can't use wide cut fuels in the CF-34 family (gasolene-kerosene) but if TS-1 is equivalent to Jet A there is a good chance it's approved for a particular airplane, but don't be surprised if there is a temperature limitation or other restriction.


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How can the same runway have two different gradients?
In an unrelated answer rbp linked to this Atlanta airport info page, and runway 8R/26L caught my eye. If I understand correctly, these two runways are the same piece of pavement, but refer to the use of the runway in opposite directions. According to that page, 8R has a gradient of "1.0% DOWN," but 26L has a gradient of "0.4% DOWN." It seems like a physical impossibility - if one is sloped down, the other must sloped up, right? So what am I missing?

The slope of a runway isn't always constant. In some cases, for example, if you stand at one end of the runway, you can't see the opposite end, because the runway goes up then down.
In this case, the ICAO (in the airport design manual) computes the runway slope as follows: the runway is divided into four equal segments. The average slope of each segment is computed and the total slope follows this formula:
[(slope of 1st quarter) + 1.33*(slope of 2nd quarter) + 2.33*(slope of 3rd quarter) + 3.33*(slope of 4th quarter)] / 8
The runway slope has a greater influence when the aircraft has a greater speed. Therefore, the slope at the end of the runway is given a greater weight.
In the case that you mention, if you walk from the west side of the runway to the east side of the runway, you will go up a little, then down, and end up at a lower altitude than when you started.

Great answer! Any chance you have a reference to the specific part of the ICAO manual that has this formula?

Appendix 2 of the Aerodrome Design Manual, Part 1 Runways, 3rd edition, 2006, ICAO. The formula is page A2-4.

So the formula is relevant for take off (obviously on landing the first part is most important). Is the slope less important for landing?